Big sympathy Dominie - both for your supply experience and for the silly bees who want to divert good discussion to assuage their own degree of autism.
You and I have lived through a time of massive change in schools and in society. The biggest difference is in the end goal ie jobs. The ultimate carrot n stick used to be a promise of a good 'character' and a start at a local firm. All this talk about whacking kids is from people who never had the job to do - we both know that's not a solution.
Remedial became Special Needs which became depended on having a formal 'statement of learning and behavioural difficulty' ie the kid is 'statemented'.
The litigious society we live in also contributes. It goes - he can't (listen, behave, follow instruction etc) because he's statemented - you're picking on him because he's statemented - speak to my lawyer.
In addition many families find it easier to indulge their children with phones than to enforce standards of behaviour. You will now encounter many, many children and teens who have never been gainsaid on any issue.
Not a class thing - apparently a temporary teacher at Princess Di's alma mater discovered most of her class could not be required to read, write or pay attention.
So don't beat youreself up Dominie - we had a good living from this nonsense, let's do something we enjoy now.